This invention relates to a method for producing a plastic binding used for binding sheet materials or covers containing sheet materials.
Plastic bindings such as in U.S. Pat. No. 1,970,285 have been in use for many years. Most plastic bindings are fabricated of polyvinyl chloride either homo or as a co-polymer. One of the general problems that exist is a world-wide shortage of chemical feed stocks to produce such compounds. This naturally leads to higher costs which manufacturers hope to reduce. It is desirable, therefore, to make available, if possible, a plastic binding which is less costly but will still do the job for which it is intended. One manner of doing this would be to reduce the amount of material in a plastic binding. It would be desirable to accomplish this without sacrificing any of the strength or stiffness that is required.
Traditionally plastic bindings have been manually formed by relatively simple equipment as described in U.S. Pat. Nos. 2,211,743 and 2,211,744. Here a plastic blank is heated and formed around an arbor in conjunction with a cloth wrapper. After an appropriate dwell, the cloth is removed and a cooled and now-rolled plastic binding is stripped from the arbor. This produces bindings with fingers which essentially are straight transversely across the respective fingers. As noted above, such bindings lack sufficient strength, particularly if the amount of plastic binding material is minimized.
It is also known to provide automated binding producing machines such as U.S. Pat. No. 2,273,824 which employ tubular-shaped and split-openable dies with and without internal guiding arbors to produce plastic bindings at high rates of speed. Such binding machines produce bindings with fingers which essentially are also straight transversely across the respective fingers. Consequently, the similar problem exists in that sufficient strength is lacking when the amount of plastic material utilized is minimized.